<html lang="en">
<head>
<meta charset="UTF-8">
<title>JavaScript</title>
<style>
div{
 font-size: 100;
 color: blue;
}
</style>
</head>
<body>
 <div>
 <script>
 document.write("<h1>Hello world!</h1>");
</script>
 </div>
</body>
</html>